Certain downhole operations involve placement of elements in a downhole environment, where the element performs its function, and is then removed. For example, elements such as ball/ball seat assemblies and fracture (frac) plugs are downhole elements used to seal off lower zones in a borehole in order to carry out a hydraulic fracturing process (also referred to in the art as “fracking”) to break up different zones of reservoir rock. After the fracking operation, the ball/ball seat or plugs are then removed to allow fluid flow to or from the fractured rock.
Balls and/or ball seats, and frac plugs, can be formed of a corrodible material so that they need not be physically removed intact from the downhole environment. In this way, when the operation involving the ball/ball seat or frac plug is completed, the ball, ball seat, and/or frac plug is dissolved away. Otherwise, the downhole article may have to remain in the hole for a longer period than is necessary for the operation.
To facilitate removal, such elements can be formed of a material that reacts with the ambient downhole environment so that they need not be physically removed by, for example, a mechanical operation, but instead corrode or dissolve under downhole conditions. However, while corrosion rates of, for example, an alloy used to prepare such a corrodible article can be controlled by adjusting alloy composition, an alternative way of controlling the corrosion rate of a downhole article is desirable.